Taste of Science: Fermented Beverages

By Laura Tran, C2ST Intern, Rush University

Credit: Chenfu Hsing, https://news.mit.edu/2021/living-materials-kombucha-0111

Over the last decade there has been a health craze brewing over kombucha (kuhm-boo-chuh) and other fermented drinks and food (e.g., yogurt, kefir, miso, sauerkraut, and kimchi). Like coffee and tea, kombucha has origins dating back to over 2,000 years ago. As kombucha spread across the world due to expanding trade routes, so did the number of beneficial health claims. What is kombucha and does this superfood live up to its reputation?

Kombucha¹ is a fermented drink made from green or black tea, sugar, yeast, and bacteria. This concoction of live bacteria and yeast is known as a SCOBY (symbiotic colony of bacteria and yeast). While the exact composition of each SCOBY varies, it generally contains lactic acid bacteria, acetic acid bacteria, and yeast. These are commonly found in other dairy products as well! Yogurt is known to contain a lactic acid bacteria called Lactobacillus, while  beer, wine, and bread use a yeast strain called Saccharomyces. The SCOBY is added to sweetened tea and left to ferment for a few weeks. A pellicle can form on top of the liquid, which is a layer of cellulose that the SCOBY develops when in contact with oxygen.

Fermentation is the basis for brewing kombucha. This is where science happens! Fermentation is the process in which bacteria and yeast obtain energy through the breakdown of sugars, producing ethanol (alcohol) as a byproduct. However, the alcohol is produced in small quantities (commercial kombucha teas contain less than 0.5% alcohol). The alcohol byproduct is converted to acetic acid (vinegar). Acetic acid is what gives kombucha its distinct flavor! The SCOBY also interacts with polyphenols², micronutrients in tea leaves, to create new organic compounds that lower the acidity of the drink. Carbon dioxide is also released as a byproduct in this process which gives kombucha its signature fizzy taste. Finally, the result is a slightly sweet, slightly tart beverage. 

Many people have opted to try their hand at homebrewing kombucha. Homebrewing is akin to a science experiment, as people tinker with the type of tea, components of SCOBY, fermentation time, temperature, and even the addition of other ingredients (e.g., berries, peach, ginger, mango, the possibilities are endless!). 

Traditionally, kombucha is characterized by high antioxidant potential due to the polyphenols present in tea. Antioxidants complement an everyday diet and contribute to good health. Kombucha contains B vitamins, antioxidants, and probiotics, but the drink’s nutritional content will vary. One study³ compared kombucha that was made with either green, white, red, or black tea. Green tea was characterized by the most significant antioxidant properties, followed by red, white, and black tea respectively. Studies⁴ also suggest that kombucha has antimicrobial, anti-inflammatory, and anti-carcinogenic properties in addition to boosting the health of intestinal cells in the gut. 

Despite all the health claims about kombucha, nutrition experts say there’s not enough scientific evidence yet to support most of them. Extensive research is needed to see how robust these health proponents of kombucha are. While kombucha may not quite live up to all of its proclaimed health benefits, it does generate interest in microbes and how these host-microbe interactions impact human health and our environment. Recently⁵, researchers have investigated generating living materials with programmable functionalities, inspired by bacteria and yeast used in kombucha (coined syn-SCOBY). Ideally, these living materials can sense and respond to chemical and optical cues so that they may be used in sensing environmental pollutants.

There is much to learn about the benefits of kombucha. Not only can this fermented drink be a simple, tasty complement to your diet, kombucha has the potential to culture a new wave of biomaterials.

Cheers!

References

  1. Jayabalan, R., Malbaša, R.V., Lončar, E.S., Vitas, J.S. and Sathishkumar, M. (2014), A Review on Kombucha Tea—Microbiology, Composition, Fermentation, Beneficial Effects, Toxicity, and Tea Fungus. Comprehensive Reviews in Food Science and Food Safety, 13: 538-550. https://doi.org/10.1111/1541-4337.12073
  2. Pandey, K. B., & Rizvi, S. I. (2009). Plant polyphenols as dietary antioxidants in human health and disease. Oxidative medicine and cellular longevity, 2(5), 270–278. https://doi.org/10.4161/oxim.2.5.9498
  3. Jakubczyk, K., Kałduńska, J., Kochman, J., & Janda, K. (2020). Chemical Profile and Antioxidant Activity of the Kombucha Beverage Derived from White, Green, Black and Red Tea. Antioxidants (Basel, Switzerland), 9(5), 447. https://doi.org/10.3390/antiox9050447
  4. Villarreal-Soto, S. A., Beaufort, S., Bouajila, J., Souchard, J. P., & Taillandier, P. (2018). Understanding Kombucha Tea Fermentation: A Review. Journal of food science, 83(3), 580–588. https://doi.org/10.1111/1750-3841.14068
  5. Gilbert, C., Tang, T. C., Ott, W., Dorr, B. A., Shaw, W. M., Sun, G. L., Lu, T. K., & Ellis, T. (2021). Living materials with programmable functionalities grown from engineered microbial co-cultures. Nature materials, 10.1038/s41563-020-00857-5. Advance online publication.